1. Field of the Invention
The present disclosure generally relates to integrated circuits and, more specifically, to the non-volatile storage of an image in an integrated circuit during the circuit manufacturing.
2. Discussion of the Related Art
In many cases, it is needed to permanently store an image in an integrated circuit on manufacturing of the integrated circuit. The image for example shows an identifier of the wafer on which the integrated circuit is manufactured, the position of the integrated circuit on the wafer, an identifier of the wafer batch to which the wafer of the integrated circuit belongs, etc.
Generally, to permanently store an image in the form of binary data in an integrated circuit, a ROM-type memory, an electrically erasable programmable read-only memory (or EEPROM), etc. is generally used.
A disadvantage is that the image to be stored may be unavailable at the time when the etch masks used during the integrated circuit manufacturing are defined. Further, the image to be stored may vary from one wafer to the other, especially when it shows identifiers of wafers and of wafer batches. Since the storage of data in a ROM generally requires the use of at least one specific mask for the forming of the memory cell connections, it is not compatible, for a manufacturing of circuits at an industrial scale, to have to multiply the number of masks to be used.
Further, it is desirable for the stored image to remain accessible even when the integrated circuit is disabled. As an example, when the stored image represents the batch identifier, the wafer identifier, the integrated circuit position, etc., it is generally desired to access this image when the circuit is malfunctioning, to ease the determination of the causes of this malfunction. When the image is stored in a ROM, an EEPROM, etc., it is no longer possible to read it when the circuit is no longer functional.
An example of a method for permanently storing an image at the level of an integrated circuit, enabling the stored image to remain accessible when the circuit is disabled and enabling to easily store different images from one integrated circuit to the other, comprises scanning the upper surface of the integrated circuit with a laser to etch the image in the form of patterns on a portion of the integrated circuit. However, such a method needs to be implemented separately on each integrated circuit and is thus not compatible with the manufacturing of integrated circuits at an industrial scale. Further, the images to be stored may be unavailable at the time when the laser etch method is to be implemented.